MOS MCS2529 math chip

Jules Richardson jules.richardson99 at
Sun Jul 22 18:03:18 CDT 2018

On 07/22/2018 02:35 PM, Paul Berger via cctalk wrote:
> These calculators all have 3 NiCd 
> cells in them if the batteries where already removed, you may get a clue 
> from the shell how many cells it was designed for.

Oh, fun... so, I'd found this snippet of info online the other day:

I have this calculator that I purchased sometime in the 1970's. Just today 
I pulled it out of the desk drawer and took the back off to see what type 
of batteries it had. The only thing I had to go on was the number on the 
pack (12B012). I did a Google search and came up with zilch; however, I 
slipped the pack out of the cylinder case and did some measurements. It 
appears that two NiCad size 4/5A cells would work since the size is 
identical. You would need two of these single cells and simply slip them 
into the Melcor outer case (in series) then place them into the calculator. 
I have not tried this yet, but I do intend to try it when I can get my 
hands on the 4/5A cells. Size, voltage etc. seem to be identical.

So I thought I was looking at a pack made from a pair of 1.2V cells. But I 
just revisited mine, also a 12B012, and realized that I could 
non-destructively dismantle it (I like keeping original batteries when I 
can - separate to the machine they were in, of course). Anyway *my* 12B012 
is three cells, not the two that the above info seemed to imply.

Somewhere I'd read that someone had powered one of these calcs up on 3V 
without damage, although it was a little temperamental. Deciding to risk 
that, I just tried it with a pair of 1.5V AA's and... it works!

I still don't know the original voltage of the pack in mine, I mean maybe 
it was 3.6, maybe 4.5... but at least I can see how it goes now running on 
3V, and make sure that the keys all work and such.



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